Location of the events in the Tonga-Fiji region (white stars at lower center) that give rise to anomalous shear-wave splitting, recorded at Hockley, Texas (HKT; white dot). Thin lines indicate raypaths connecting the events and HKT; thick lines indicate portions of the paths in D''. The locations of seismographic stations at Tucson, Arizona (TUC; diamond), Albuquerque, New Mexico (ANMO; triangle) and Wichita Mtn., Oklahoma (WMOK; square) are also shown. The D'' sampling of Vinnik et al. (1995) is indicated with gray shading. In the background is a shear velocity map of the lowermost mantle (Grand et al., 1997).